Connected: An Internet Encyclopedia
RFC 1772 - 7. Required set of supported routing policies

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### 7. Required set of supported routing policies

Policies are provided to BGP in the form of configuration information. This information is not directly encoded in the protocol. Therefore, BGP can provide support for very complex routing policies. However, it is not required that all BGP implementations support such policies.

We are not attempting to standardize the routing policies that must be supported in every BGP implementation; we strongly encourage all implementors to support the following set of routing policies:

1. BGP implementations should allow an AS to control announcements of BGP-learned routes to adjacent AS's. Implementations should also support such control with at least the granularity of a single address prefix. Implementations should also support such control with the granularity of an autonomous system, where the autonomous system may be either the autonomous system that originated the route, or the autonomous system that advertised the route to the local system (adjacent autonomous system). Care must be taken when a BGP speaker selects a new route that can't be announced to a particular external peer, while the previously selected route was announced to that peer. Specifically, the local system must explicitly indicate to the peer that the previous route is now infeasible.

2. BGP implementations should allow an AS to prefer a particular path to a destination (when more than one path is available). At the minimum an implementation shall support this functionality by allowing to administratively assign a degree of preference to a route based solely on the IP address of the neighbor the route is received from. The allowed range of the assigned degree of preference shall be between 0 and 2^(31) - 1.

3. BGP implementations should allow an AS to ignore routes with certain AS's in the AS_PATH path attribute. Such function can be implemented by using the technique outlined in [2], and by assigning "infinity" as "weights" for such AS's. The route selection process must ignore routes that have "weight" equal to "infinity".

Next: 8. Interaction with other exterior routing protocols

Connected: An Internet Encyclopedia
RFC 1772 - 7. Required set of supported routing policies